The US Department of Agriculture reports that avian flu has now spread to 30 states. Avian influenza (AI) is caused by an influenza type A virus which is classified by a combination of two groups of proteins: hemagglutinin or “H” proteins, of which there are 16 (H1–H16), and neuraminidase or “N” proteins, of which there are 9 (N1–N9). AI viruses